Summary
Nutrient-rich sewage can pollute and overnutrify estuary waters.
Overnutrified estuary waters cause algae to proliferate.
Abundant algae can be a food source for microorganisms that are toxic to fish.
These microorganisms kill most fish in the estuary.
Overnutrified estuary waters cause algae to proliferate.
Abundant algae can be a food source for microorganisms that are toxic to fish.
These microorganisms kill most fish in the estuary.
Very Strongly Supported Conclusions
Abundant algae in an estuary can cause most fish in the estuary to die.
Overnutrified estuary waters can cause most fish in the estuary to die.
Nutrient-rich sewage pollution can cause most fish in an estuary to die.
Overnutrified estuary waters can cause most fish in the estuary to die.
Nutrient-rich sewage pollution can cause most fish in an estuary to die.
A
Fish in an estuary that has been polluted by sewage are generally more likely to die from pollution than are fish in an estuary that has been polluted in some other way.
Unsupported. Nutrient-rich sewage can kill most fish in an estuary, but we don’t know that it’s more likely to than other forms of pollution.
B
In estuary waters that contain abundant algae, microorganisms that are toxic to fish reproduce more quickly than other types of microorganisms.
Unsupported. Abundant algae can be a food source for toxic microorganisms, but we don’t know that it causes toxic microorganisms to reproduce more quickly than other types of microorganisms.
C
Nutrients and other components of sewage do not harm fish in coastal estuaries in any way other than through the resulting proliferation of toxic microorganisms.
Unsupported. Nutrient-rich sewage can harm fish in estuaries by causing algae to grow, which feeds toxic microorganisms. But it might harm fish in other ways too.
D
Algae will not proliferate in coastal estuaries that are not polluted by nutrient-rich sewage.
Unsupported. Overnutrified waters do cause algae to proliferate, but it might proliferate in other conditions too.
E
Overnutrifying estuary waters by sewage can result in the death of most of the fish in the estuary.
Very strongly supported. Overnutrified estuary waters cause algae to proliferate, which can then feed toxic microorganisms that kill most fish in the estuary. So, nutrient-rich sewage pollution can cause the death of most fish in an estuary.
Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that an overabundance of algae is harmful to smaller fish in this pond. This is based on the fact that over the past 15 years, the few times that the author has seen a lot of dead small fish has coincided with the times that he has noticed unusually large amounts of algae in the water.
Identify and Describe Flaw
The author assumes that the correlation between lots of dead small fish and lots of algae is explained by algae causing harm to the small fish. This overlooks alternate explanations for the correlation. Perhaps there’s a third factor that causes both the algae and the dead fish. The author also assumes that his own observations of the timing of dead small fish and lots of algae is representative of the general pattern of dead small fish and lots of algae in the pond.
A
presumes, without providing justification, that smaller fish are somehow more susceptible to harm as a result of overabundant algae than are larger fish
The author never compares the effects of algae to the effects of larger fish.
B
fails to consider that the effects on smaller fish of overabundant algae may be less severe in larger bodies of water with more diverse ecosystems
The author’s conclusion doesn’t concern other bodies of water besides “this pond.”
C
ignores the possibility that the same cause might have different effects on fish of different sizes
The author’s conclusion only concerns the effects of algae on “smaller fish.” Fish of other sizes are not relevant to the argument.
D
ignores the possibility that the overabundance of algae and the deaths of smaller fish are independent effects of a common cause
This possibility presents an alternate explanation for the author’s evidence. Perhaps algae isn’t harmful to smaller fish, but rather the algae and deads of small fish are both results of some other cause.
E
ignores the possibility that below-normal amounts of algae are detrimental to the pond’s smaller fish
The author didn’t say that below-normal amounts of algae are not harmful to smaller fish. The conclusion is that overabundance of algae is harmful, but this doesn’t imply that the author thinks less than abundant algae isn’t harmful.
"Surprising" Phenomenon
Why have there been so many recorded tornadoes since 1953 if the climate has not made them any more likely to form?
Objective
Any hypothesis resolving this discrepancy must state a reason for tornadoes to have tripled despite the constant climatic factors. It will explain why tornadoes since 1953 are much more likely to be seen or give a reason for the actual number of tornadoes to have tripled.
A
The factors affecting the creation of tornadoes were not well known to meteorologists before 1953.
This does not explain the increase in recorded tornadoes. Meteorologists know those factors have not changed since 1953, regardless of whether they understood those factors in 1953.
B
The intensity of the average tornado is greater now than it was in 1953.
This introduces a new mystery without resolving the discrepancy at hand. A greater average intensity does not explain a greater number of tornadoes.
C
The number of tornadoes recorded annually has increased only slightly in the last five years.
This offers no reason why the number of recorded tornadoes has tripled since 1953. It does not address the period between 1953 and five years ago.
D
The amount of property damage done by tornadoes has grown substantially since 1953.
This does not explain why more tornadoes have been recorded since 1953. It is not stated that more tornadoes have destroyed property, only that the total damage caused by those tornadoes has been greater.
E
Many more citizens are helping authorities detect tornadoes now than in 1953.
This explains why the number of tornadoes recorded has tripled since 1953. More people are looking for tornadoes, making them more likely to be spotted, even if their overall numbers have not changed.